1. Field of the Invention
The present invention concerns a computed tomography apparatus of the type having a gantry at which components of an acquisition system are mounted such that the gantry and the components rotate around a system axis, a stationary part in which the gantry is supported such that it can tilt, and a cooling device for cooling the components mounted at a gantry by means of an air flow.
2. Description of the Prior Art
Three-dimensional slices images of an examination region of a patient are generated with computed tomography apparatuses for diagnosis or therapy the use of x-rays. At typical computed tomography apparatus has a gantry for mounting components of an acquisition system arranged such that they can rotate around a system axis, and a stationary part in which the gantry is supported. To acquire projections of an examination region of a subject, the acquisition system has, as one of the components a component a radiator in the form of an x-ray tube and, as another of the components, a detector arranged opposite the x-ray tube. Projections from a number of different projection directions at various positions along the examination region are acquired by a rotation of the gantry simultaneously with a continuous feed in the direction of the system axis of a patient on a mobile platform on a support device. The projections acquired in this manner with a helical scan are transmitted to a computer and a three-dimensional slice image is calculated (computed) therefrom which, for example, can be presented on a display unit.
A fundamental heat problem is present in all computed tomography apparatuses because 99% of the electrical energy used in the generation by x-ray radiation of the x-ray tube is converted into heat energy. To ensure proper operation of the computed tomography apparatus, it is necessary to dissipate the heat from the gantry in order to avoid overheating the x-ray tube. This is particularly the case when high x-ray power is required for scanning the examination region. Not only the x-ray tube, but also the detector, must be cooled during the operation of the computed tomography apparatus, because otherwise the signal-to-noise ratio of the acquired measurement values degrades with increasing temperature of the detector, which designates the image quality of the reconstructed slice images.
Cooling of the components arranged on the gantry can be achieved with high expenditure because the gantry normally rotates continuously around the examination region during the entire radiological examination. The dissipation of the heat during operation of the computed tomography apparatus proves to be complicated and problematic due to this continuously present rotation movement.
A computed tomography apparatus that has a cooling device for cooling the components of the acquisition system arranged on the gantry by means of an air flow is known from U.S. Pat. No. 4,969,167. The stationary part and the gantry of the known computed tomography apparatus are enclosed by a common housing. A removable housing wall, which is arranged parallel to the acquisition plane and serves to cover the internal components of the computed tomography apparatus thereby, has an air feed channel. The air feed channel is arranged in the immediate proximity of the rotating acquisition system and extends in a circle along the periphery of the gantry. To cool the x-ray tube and the detector, the air feed channel contains along its periphery a number of outlet openings via which an air flow for cooling is dispensed onto the rotating components of the gantry. This air flow is produced by a generator that is associated with the stationary part of the gantry and is connected to the air feed channel. The cooling is achieved by the openings in the air feed channel being arranged close to one another and having only a slight separation from the rotating gantry.
Computed tomography apparatuses of the more recent generation have a gantry that is supported such that it can be tilted relative to the stationary part of the computed tomography apparatus. The gantry and the stationary part thus have separate housings. In contrast to the computed tomography apparatus described above, the components of the acquisition system are cooled by an air flow fed into the housing of the gantry, with outlet openings being provided above the housing from which the air flow can be exhausted (discharged). The air flow is thus dissipated into the examination room in different directions depending on the tilt of the gantry relative to the stationary part of the computed tomography apparatus.